A sensor element which has a pair of positive and negative detection electrodes disposed on a surface of an insulation body as a detecting portion and a cover body configured to cover an opening of a cylindrical housing. The cover body is provided with gas inlet and outlet holes via which the measuring gas is introduced and discharged. The pair of detection electrodes have a plurality of wire electrodes. The wire electrodes electrically connected to the positive electrode and the wire electrodes electrically connected to the negative electrode are alternately arranged in parallel. Any one of a first insulation layer which is a narrow electrode interval Dn and a second insulation layer which is a wide electrode interval Dw, arranged between adjacent wire electrodes, and the first insulation layer arranged in a center part of the detecting portion.